How to make nice curvy contour on high detailed (sculpted) mesh?
the reason of that resides on the actual geometry of your mesh, seems to have to many vertex and a very nested topology. I recomend you to try reduce your vertex acount from the beggining and use the subdivision surface modifier it'll round your shapes but it'll still will follow the topologhy. 
You can try to use remesh modifier or decimate modifier to reduce vertex number. But you'll loose all the sculpted allready details. 
good luck!